Aspirator devices which rely on the venturi effect to create a vacuum and draw a first liquid into a second pressurized liquid flowing past an orifice are well known in the art. For example, Published PCT Patent Application No. WO 91/16138 to Horvath et al. teaches a precision-ratioed fluid-mixing device and system that uses an aspirator device to meter a quantity of a liquid concentrate such as a cleaner liquid disinfectant into a pressurized stream of water from a household water plumbing line to obtain a ready-to-use aqueous cleaning or disinfecting solution. Horvath et al. use a combination of two orificed metering elements which together limit the flow of the concentrate into the pressurized stream of water. One such metering orifice is located in the aspirator itself (cylindrical orifice 230 of nominal diameter 0.080 inches) and the other is a removable metering element located in the diptube extending into the container holding the liquid concentrate. Horvath et al. teach that the nominal diameter of the orificed inlet 188 in the removable metering element could range between 0.006 inches to 0.071 inches.
A commercial system of the type described in the Horvath et al. patent application has been sold since 1991 under the brand name of SOLUTIONS CENTER.TM. by the S. C. Johnson Professional Products Division of S. C. Johnson & Son, Inc. of Racine, Wis. The SOLUTIONS CENTER.TM. system also uses a combination of two metering elements, but one metering element of either about 0.048 inches or 0.103 inches in diameter is molded into the top of an apertured plug pressed into the neck of the plastic concentrate container. A removable metering element located in the diptube extends into the container from the apertured plug and is serially connected to the other metering element in the plug. The removable metering element used depends upon the product to be dispensed and thus the dilution ratio desired. The orifices in the removable metering elements range from 0.005 inches to 0.045 inches in diameter. The apertured plug is connected to a tube leading to the venturi in the aspirator device so that the contents of the liquid concentrate container are drawn into the flowing stream of water when a valve is opened by pressing a button to start the flow of water through the aspirator. Since the concentrate container (additive liquid) has both metering orifices, the user simply attaches a concentrate container to the system and does not have to select a metering orifice to obtain a properly diluted solution.
Another example of commonly known aspirator device is a garden hose-end sprayer which is used to apply lawn fertilizers and insecticides. One example of such a device is shown in U.S. Pat. No. 4,068,681 to McNair et al. McNair et al. teach a hose-end sprayer that has a reservoir container that is filled with a dry dissolvable solid lawn chemical. The reservoir container is attached to the device and automatically fills with water when water flows through the hose. A diptube in the container is connected to an aspirator that has an upper orifice and a closed opposite end containing a series of small orifices. The device also has a water bypass line which permits water to be forced into the reservoir container that is filled with the solid chemical. During filling of the reservoir container, the pressure of the water coming through the aspirator forces water backwards through the diptube into the reservoir container and out through the small orifices located in the bottom of the diptube. The result is a series of high velocity water streams that agitate the dry chemical in the bottom of the container and assist in dissolving the chemical in the water being admitted.
The improvement described by McNair et al. relates to a valve system located in the upper part of the reservoir container. Once the container is filled with water, the valve closes to stop the escape of air from the container through the valve. A small amount of water is forced into an opening that then reverses the flow of water through the diptube. A small amount of the dissolved chemical is drawn through the small orifices in the bottom of the diptube and up through the diptube to a metering orifice into the main water stream by way of the venturi effect. The metering function appears to be handled by the orifice near the aspirator rather than by the small orifices at the opposite bottom end of the diptube. Further metering can also be accomplished by another metering jet.
U.S. Pat. No. 4,058,296 to Wetherby teaches the use of check valves in the bottom of the diptube in an aspirator device to prevent backflow of the pressurized liquid into a liquid concentrate into the liquid concentrate container. Column 1, lines 18-43 cites as prior art a certain mixing apparatus that uses a bypass conduit arrangement in combination with, among other things, a series of conduit restrictions. No reference is given to any specific patent that might describe such a system. Such references may be to U.S. Pat. Nos. 3,104,823 and 3,181,797 to Hayes that describe aspirator devices for blending liquids which use restrictors in the form of bushings. The restrictors are said to provide a pressure drop in the conduit system that is divided into two separate paths comprising a main conduit and a bypass conduit. These bushings or restrictors are used to divide up the flow of the diluted concentrate provided by the aspirator devices.
For reasons of economy and efficiency, it is becoming more and more desirable to use dilution systems that use highly concentrated liquids that require high dilution ratios such as from about 1:500 to 1:2,500 parts by volume of the concentrate liquid to the main liquid such as water. Accurate dilutions are important to avoid the waste of concentrate that inevitably occurs when the liquid concentrate is manually measured out into a quantity of main liquid such as water. Use of too much concentrate can also have detrimental effects such by leaving unwanted residues of the active ingredients on surfaces being treated. For example, a volume dilution ratio of 1:256 requires the careful measurement of 0.5 ounces of concentrate and dissolving that concentrate in 1 gallon of water. To achieve a volume dilution ratio of 1:512, 0.25 ounces of concentrate must be added to a gallon of water. If only a quart of diluted liquid is desired, then the quantity of concentrate to be measured is very small indeed. This is simply not convenient for a maintenance user and waste of the concentrate is almost inevitable.
An even more important consideration is when a sanitizer or disinfectant liquid is being prepared. Accurate dilution of the concentrate is critical to obtain a solution which will have the required disinfecting properties. If the solution is too dilute, then bacteria will not be adequately removed by the solution. That can create problems in a hospital or other institutional setting where proper removal of bacteria is important. Since inaccurate dilutions can create problems, conscientious maintenance personnel tend to use too much concentrate which results in waste of the concentrate.
Molded plastic components that are often made by injection molding are often used in aspirator devices of the above type for reasons of economy and simplicity of manufacture. High dilution ratio devices require the use of restrictors containing very small orifices. There is a limit as to the diameter and length ("land") of an orifice that can be injection molded because the pin used to form the orifice can be warped or broken as plastic is injected at high pressure if the diameter of pin is too small for its length to handle the pressure. Generally, orifices of smaller than about 0.005 inches in diameter with land lengths longer than the diameter cannot be injection molded from plastic. The land length is important to the dilution ratio of liquid concentrate to main liquid. The viscosity of the liquid concentrate affects its flow through the orifice in the restrictor. Generally, a longer land length is needed for higher liquid dilution ratios, but this is not technically feasible for a single restrictor because of molding technology limitations. A practical dilution ratio limit for a single restrictor is about 1:750.
Use of additional operations such as laser drilling to create the desired orifice in a plastic restrictor is often not effective because the heat of the laser melts the plastic and makes creates an undesirable variability in the diameter and land length of the plastic restrictor. Drilling with fine drills is so labor intensive and time consuming that it is typically not economical to commercially make restrictors by such a method.
Thus, there is still a need for an improved aspirator device for blending two liquids that can accurately provide volume dilution ratios of a liquid concentrate to a main liquid such as water of from about 1:500 to 1:2,500.